1. Field of the Invention
The present invention relates to hydrocyclones for separating a slurry into separate constituents by density and particle size and to separator assemblies utilizing the hydrocyclones. More particularly, the present invention relates to an improved hydrocyclone which is not under tensile or compressive stress when it is installed in a separator assembly.
2. Description of Related Art
It is well known to use hydrocyclones to separate particles of different sizes carried in a fluid stream. The particle separation achieved is governed by various factors including the dimensions of the hydrocyclone, the density of the suspension to be separated and its inlet pressure. To achieve some separations, it is necessary to use extremely small hydrocyclones which have a correspondingly small throughput. In order to achieve a commercially viable throughput, it is then necessary to employ a multitude of such hydrocyclones assembled in parallel. The most effective use of hydrocyclones is in separator assemblies with multi-stage operations. In the corn wet milling industry, hydrocyclones are used in starch wash operations, where multi-stage counter-current assemblies are preferred for purification of starch by removal of contaminants to the light phase, such as soluble and insoluble proteins, fine fibers, etc.
One type of a known separator assembly which uses a multitude of hydrocyclones is illustrated in FIGS. 12 to 14 of the accompanying drawings, in which:
FIG. 12 is a schematic, partially sectioned side elevational view of part of the prior art separator assembly;
FIG. 13 is a section taken on line 13--13 of FIG. 12; and
FIG. 14 is an enlarged axial-sectional view of a hydrocyclone incorporated in the assembly of FIGS. 12 and 13.
The prior art assembly of FIGS. 12 to 14 will now be described in brief with an emphasis on those parts which lead to an understanding of the present invention.
With reference to FIG. 12, a part of a separator assembly generally indicated as 10 is shown. Separator assembly 10 has a generally cylindrical casing 12, only one end portion of which is shown, and which is constituted by annular walls 14 and end walls 16. Walls 14, 16 are clamped together by longitudinally extending bolt members 18 and end clamp members (not shown) with the interposition of pairs of transverse round partitions 20, 22 extending perpendicular to casing 12 axis and clamped between adjacent edges of annular walls 14. Only one pair of partitions 20, 22 is shown. Casing 12 may include any number of such pairs of partitions 20, 22. Partitions 20, 22 each have outer faces 24, 26 and opposing inner faces 28, 30, respectively.
With reference to FIGS. 12 and 13, each partition 20, 22 has a plurality of circular apertures 32, 34, respectively, arranged in regular two dimensional arrays. Apertures 32, 34 in each pair of partitions 20, 22 are axially aligned. Not all of apertures 32, 34 are shown in FIG. 13, for clarity of illustration.
Partitions 20, 22 define central inlet chamber 36 between their opposing faces 28, 30 and two outlet chambers 38, 40 adjacent their outer faces 24, 26, respectively. An inlet duct 42 opens into central inlet chamber 36 while outlet ducts 44, 46 open from outlet chambers 38, 40, respectively.
Inlet chamber 36 does not communicate directly through apertures 32, 34 in partitions 20, 22 with outlet chambers 38, 40 but through hydrocyclones 48, each of which extends parallel to the chamber 36 axis. with reference to FIG. 14, each hydrocyclone 48 is formed in two cooperatingly screw threaded parts 50 and 52. Part 52 has an underflow end 54 and an opposite overflow end 56. Parts 50 and 52 have substantially cylindrical outer surfaces 58 and 60, each formed with annular grooves 62 and 64 therein and having flange 66 and end flange 68, projecting from their ends. O-rings 70 are provided to fit into each of the cooperating grooves 62 and 64.
When interengaged, the inner surface of part 52 defines a frusto-conical internal separating chamber 72 to extend and taper between overflow end 56 and underflow end 54 thereof. Surface 60 has inlet cavity 74 formed at overflow end 56 of part 52. Each inlet cavity 74 has a rectangular tangential inlet opening 76 into it from central chamber 36.
Continuing with FIG. 14, vortex finder 78 projects through inlet cavity 74, terminating axially downstream of tangential inlet opening 76 and defines a first axial outlet 80, the overflow outlet, which communicates with the adjacent outlet chamber 38 (shown in FIG. 12) of assembly 10 while the opposite underflow end 54 of hydrocyclone 48, clamped in the opposite partition 22, has a second axial outlet 82, the underflow outlet, which communicates with outlet chamber 40. Vortex finder 78 also defines a helical channel 84 (not shown) the beginning of which faces inlet opening 76.
When assembled in assembly 10, hydrocyclones 48 extend through and are sealed in apertures 32 and 34 by means of O-rings 70 fitted in grooves 62 and 64, which create seals between central chamber 36 and outlet chambers 38 and 40, respectively. Inlet cavity 74 is located adjacent partition 20. Flange 66 of part 50 abuts outer face 24 of partition 20, while end flange 68 of part 52 abuts outer face 26 of part 22.
In use of assembly 10, a suspension to be classified is pumped under pressure into central inlet chamber 36 through inlet duct 42 and is forced through tangential inlet openings 76 of hydrocyclones 48 into their frusto-conical chambers 72. Helical channel 84, defined by vortex finder 78, ducts the inlet flow circumferentially and axially toward frusto-conical chamber 72, thereby reducing the turbulence that would arise in a purely cylindrical inlet cavity. In each chamber 72, the suspension is separated into two flows. The first, termed the overflow, contains the finer particles and exits through first axial outlet 80 into chamber 38 while the second, termed the underflow, containing coarser particles, exits through the opposite outlet 82 into chamber 40. Naturally, the combined overflows from hydrocyclones 48 exit from assembly 10 through outlet duct 44 while the combined underflows exit through outlet duct 46.
Separator assembly 10 described in relation to FIGS. 12 to 14 achieves good separation, but has certain problems and disadvantages.
A first problem is in the assembly of hydrocyclones 48. In order to enable hydrocyclones 48 to be inserted and firmly held in their positions of use, extending through partitions 20 and 22, parts 50 and 52 are inserted through opposing apertures 32 and 34 from outer faces 24 and 26 of partitions 20 and 22, respectively, to meet in central chamber 36 and are screwed tightly together until flanges 66, 68 abut outer faces 24 and 26. In order to screw parts 50 and 52 together, each end needs to be gripped by a suitable tool to enable adequate tightening. Access to outer faces 24 and 26 of both partitions 20 and 22 simultaneously, however, can be problematical and this process is further complicated by the fact that vortex finder 78 is formed as a separate part which is inserted into inlet opening 76 defined by hydrocyclone part 50 through its screw-threaded end which mates with part 52. The insertion of vortex finder 78 is an awkward operation since it is a close fit in its seat in part 50 but is small and not easy to manipulate. Also, although it is shaped to key with its seat in one specific orientation, there is no positive engagement between the two parts, and vortex finder 78 is held in position by clamping between the two interengaged parts 50 and 52. All of the parts must therefore be very precisely dimensioned in relation to each other and there is always a possibility of vortex finder 78 being accidentally shaken from its seat during the screwing together of parts 50 and 52.
An alternative prior-art hydrocyclone, disclosed in connection with a Type C "Clamshell" housing in a 1976 Dorr-Oliver brochure, used in a similar assembly as that shown in FIG. 12, is easier to assemble. Each Type C 10 mm hydrocyclone is formed in three parts, each injection molded in nylon. The components are a major annular body part, a tubular vortex finder and an apex nut which is hexagonal and internally threaded to mate with corresponding external threads on the annular body at the underflow end. The vortex finder has a hexagonal head forming a flange and a parallel threaded section below the head which threadably mates with corresponding threads internal to the annular body at the overflow end. The body can be inserted through the corresponding holes in the two partitions from the overflow side until the vortex finder head, serving as a stop member, abuts the outer face of the partition on the overflow end and the opposite underflow end projects through the other partition, on the underflow end. The apex nut is then screwed onto the projecting underflow end of the body and tightened into contact with the outer face of the partition on the underflow end, so that the hydrocyclone is clamped to the outer surfaces of the partitions, thereby placing the hydrocyclones under tension.
A major problem with this alternative hydrocyclone arises. Precisely because of the screw-fitting of the vortex finder, it is difficult to provide a helical surface on the vortex finder, as will be described below with respect to the present invention, to improve the fluid flow into the hydrocyclone separating chamber. It is difficult because the vortex finders and hence the helical surface cannot be aligned accurately with the inlet. The hydrocyclone must, therefore, have relatively smaller dimensions and a correspondingly smaller throughput to achieve a given degree of separation. Considering assemblies including tens, or even a hundred or more, of such hydrocyclones, it will be appreciated that even slight differences in throughput have a great effect on the overall performance of the assembly.
A further problem with this alternative construction is that, in use, the suspension to be separated is pumped into the central chamber of the separator assembly under considerable pressure which may cause outward deflection of the partitions, thus putting the hydrocyclones under additional strain, or tension. The strain reduces the working life of the hydrocyclones.
Also, because both of the O-rings in this construction are the same size, the distal O-ring, which has to be pulled through two holes of the separator assembly on disassembly, often breaks or is damaged.
Furthermore, the alternative prior art hydrocyclone described above is used particularly in the food industry in a counter-current washing circuit in which clean wash water pumped in at one end separates gluten from corn starch. The clean corn starch exiting with the underflow while the gluten is washed out with the overflow. A further problem that arises with this use is that the hydrocyclones are made from NYLON, which reacts with sulfur dioxide used as a preservative in the corn starch slurry and embrittles over the years. The combination of embrittlement and strain can lead to fracture of the hydrocyclone body as well as reduced capacity and performance, leading to production losses and to incurment of relatively high replacement costs. Another problem with the use of NYLON as a material of construction for hydrocyclones is that the material tends to expand on contact with the slurry of water and processed corn during separation, and in a non-uniform manner.
Another type of separator assembly which uses a multitude of hydrocyclones is illustrated in "The Dorr Clone Hydrocyclone" sales brochure, 1976. These assemblies, in which one or both of the wall members is removable, are designated as "Type TM". The TM assemblies utilize 10 mm hydrocyclones to wash starch in corn wet milling operations. An adaptation of this assembly also is described in U.S. Pat. No. 5,499,720 and a related patent is U.S. Pat. No. 5,388,708.
Each type TM hydrocyclone is formed in two parts, each injection molded from nylon, comprising a major annular body part and a tubular vortex finder, which fits by insertion into the body part. The major annular body part extends between its overflow end and opposite underflow end. The body part has an exterior defined by a semi-annular flange at its overflow end, which connects to a relatively short cylindrical portion of a smaller diameter than the flange. The short cylindrical portion further connects to a frusto conical portion which tapers toward an annular radially projecting stop member, which has a diameter approximately equivalent to that of the flange. The stop member connects to a cylindrical boss of a smaller diameter which in turn connects to relatively short frusto-conical transition portion. The transition portion connects to a frusto-conical spigot which tapers to its apex at the underflow end. The semi-annular flange has a rectangular opening bounded on three sides therein connecting to a further rectangular opening, also bounded on three sides. formed in the relatively short cylindrical portion. A rectangle bounded on all four sides, constituting a tangential inlet opening, is formed by cooperation of the body part and the vortex finder. The vortex finder is provided with a frusto-conical guide surface, which projects and extends through the inlet chamber and terminates axially downstream of the tangential inlet when assembled with the body. These hydrocyclones are held in place by being compressed between their respective partition plates.
This separator assembly achieves good separation, but has certain problems and disadvantages.
These cyclones are used particularly in the food industry, particularly in corn wet milling, in a counter-current washing circuit in which clean wash water pumped in at one end separates gluten from corn starch, the clean corn starch exiting with the underflow while the gluten is washed out with the overflow. A problem that arises with this use is that the hydrocyclones are injection molded from NYLON. The NYLON reacts with sulfur dioxide, used as a preservative in the corn starch slurry, and embrittles over the years. The combination of embrittlement and compression of the cyclones between the plates can lead to fracture of the hydrocyclone body as well as reduced capacity and performance, leading to production losses and to incurment of relatively high replacement costs.
The capacity and performance of the hydrocyclones is further limited due to the overall external and internal configuration of the hydrocyclone, which is the key parameter for optimal operation of hydrocyclones. The vortex finder is not provided with a helical guide surface, which would improve the fluid flow into the hydrocyclone separating chamber. The hydrocyclones, therefore, have a relatively small throughput to achieve a given degree of separation. Considering assemblies including tens, or even a hundred or more, such hydrocyclones, it will be appreciated that even slight differences in throughput have a great effect on the overall performance of the assembly.
The present invention, therefore, seeks to provide hydrocyclones particularly of a type usable in the assemblies of the general type described above. An object of the present invention is to provide hydrocyclones which overcome the drawbacks and disadvantages of the prior art as discussed above.
An object of the present invention is to provide hydrocyclones which are simpler to assemble and install, as well as to disassemble for repair or maintenance, than previously known hydrocyclones. The invention provides a distal O-ring having a smaller diameter than the proximal O-ring and this resolves the problem of breakage of the distal O-ring which is caused by the prior art construction. Furthermore, the hydrocyclones of the invention are installed in a separator assembly by pushing them into holes that are not threaded, thus substantially reducing the cost of the assembly and the hydrocyclones as well as simplifying assembly and disassembly.
Another object of the present invention is to provide hydrocyclones having a larger internal diameter and a better throughput for a given size of hydrocyclone, and thereby increase the capacity of the overall multi-cyclone separator assembly.
A further object is to provide hydrocyclones which are not under any tensile or compressive stress when they are installed in a separator assembly and which have a longer working life than the prior art hydrocyclones described.
Other objects of the present invention will become apparent from the summary and detailed description which follows.